1. Field of the Invention
The present invention relates to wireless communication systems and in particular to an adaptive wireless receiver that supports multiple standards and/or multiple frequency bands.
2. Description of the Related Art
Currently, the increase demand for wireless communication systems has resulted in continuing development of wireless receivers. The receivers are commonly employed in radio frequency (RF) signal transmission. In the wireless communication field, the receivers usually are capable of receiving RF signals through an antenna. The receivers convert these RF signals to desirable intermediate frequency (IF) signals before they are converted to a baseband frequency. These IF signals are then transferred to their destinations where the IF signals will be used.
FIG. 1 illustrates a block diagram of a prior art receiver 100. The receiver 100 usually is composed of an antenna 110, a bandpass filter (BPF) 120, a RF front-end unit 130, a demodulator 140 and a processor 150. After being received by the antenna 110, RF signals are filtered by the BPF 120. The RF front-end unit 130 performs the tasks of down-translating the RF signals from high frequency to a specific IF, i.e., a low frequency. The demodulator 140 will demodulate the IF signals from the RF front-end unit 130 and the processor 150 will further process the IF signals based upon the requirements of the applications. Many topological configurations have been developed for the receivers 100 to satisfy different requirements of various applications, for example, zero IF (ZIF) receiver and low IF (LIF) receiver. The ZIF receiver and the LIF receiver are both suitable for high integration.
FIG. 2 illustrates a prior art ZIF wireless receiver 200. A RF frond-end 230 is included in the ZIF wireless receiver 200. The RF front-end unit 230 can be composed of a low noise amplifier (LNA) 231, down-conversion mixers 232 and 233, lowpass filters (LPFs) 234 and 235, analog-to-digital converters (ADCs) 236 and 237. The ZIF wireless receiver 200 can translate the received RF signal to baseband frequency centered around the DC's frequency directly with an I/Q down-conversion. The cutoff frequency of the LPFs 234 and 235 is half of that of the bandwidth of the desired channel. The ZIF wireless receiver 200 has many advantages, for example, high integration. Additionally, the output of the ZIF wireless receivers 200 is an I (in-phase) and Q (qradrature-phase) signal without any carrier signal. However, using the two LPFs 234 and 235 for channel selection in both I/Q paths requires a great silicon area, especially for low band-width and low noise applications. As a result, the complexity and cost of the integrated circuit where the ZIF wireless receiver 200 is embedded will be greatly increased. In addition, the mismatch between the I path and the Q path and a DC offset caused by the mix between the RF signal and the LO signal can adversely affect the performance of the ZIF wireless receiver 200.
FIG. 3 depicts a prior art LIF wireless receiver 300. The LIF wireless receiver 300 includes a RF front-end unit 330 that consists of a LNA 331, down-conversion mixers 332 and 333, a filter 334, a combiner 335 and an ADC 336. The LIF wireless receiver 300 translates the received RF signal to a specific lower intermediate frequency signal that is somewhat away from the baseband frequency. The filter 334 can filter out an image (i.e., reject an image) included in the IF signal. Two components of the filtered IF signal in the I and Q paths are combined (i.e., added or subtracted) by the combiner 335 and then the filtered IF signal will be converted from analog to digital by the ADC 336 and demodulated by the demodulator 140. The output of the LIF wireless receiver 300 includes a carrier signal. The combiner 335 can be included in the filter 334. In one embodiment, the filter 334 can be an image rejection filter. The main drawback for the LIF wireless receiver 300 is the low IRR (image rejection rate) caused by the mismatch between the I and Q paths, which greatly limits the performance of the receiver system.
In various applications, for example, a mobile digital TV, there are different operating standards with different natures, for example, DVB-H, T-DMB and ISDB-T. To support all these different standards, the ZIF and LIF topologies should be integrated into one single silicon circuit. However, because of the incompatibility between the ZIF and LIF topologies, more tuners are required to support these different standards in traditional solutions. Furthermore, the reuse of hardware is very limited in the traditional solutions. Hence, the performance of the receiver system is limited and the silicon area of the integrated circuit will be significantly expanded when both topologies are included.
It is thus desirous to have an apparatus and method that provide an adaptive wireless receiver supporting multiple standards and/or multiple frequency bands with reduced silicon area, simple configuration and high integration. It is to such apparatus and method the present invention is primarily directed.